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Community Exposure Following a Drip-Application of ChloropicrinTerrell Barry a; Michel Oriel b; MaryLou Verder-Carlos b; Louise Mehler b; Susan Edmiston b; MichaelO'Malley cd

a Environmental Monitoring Branch, Department of Pesticide Regulation, California EPA, Sacramento,California, USA b Health and Safety Branch, Department of Pesticide Regulation, California EPA,Sacramento, California, USA c Health and Safety Branch, Department of Pesticide Regulation,California EPA, Davis, California, USA d Occupational Health Services, University of California, Davis,California, USA

Online publication date: 21 January 2010

To cite this Article Barry, Terrell, Oriel, Michel, Verder-Carlos, MaryLou, Mehler, Louise, Edmiston, Susan and O'Malley,Michael(2010) 'Community Exposure Following a Drip-Application of Chloropicrin', Journal of Agromedicine, 15: 1, 24— 37To link to this Article: DOI: 10.1080/10599240903389599URL: http://dx.doi.org/10.1080/10599240903389599

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Journal of Agromedicine, 15:24–37, 2010Copyright © Taylor & Francis Group, LLCISSN: 1059-924X print/1545-0813 onlineDOI: 10.1080/10599240903389599

24

WAGR

Community Exposure Following a Drip-Application of Chloropicrin

Community Exposure Following a Drip-Application of Chloropicrin Terrell Barry, PhDMichel Oriel

MaryLou Verder-Carlos, DVM, MPVMLouise Mehler, MD, PhD

Susan EdmistonMichael O’Malley, MD, MPH

ABSTRACT. Objectives. To evaluate illnesses resulting from community exposure to chloropicrin onOctober 5, 2005, in the agricultural community of Salinas, California. Methods. A cross-sectionalinterview survey was conducted of 142 households downwind from the application site in neighbor-hoods that were sources of emergency calls. A total of 439 residents of the 142 households in affectedneighborhoods and 1 emergency responder were interviewed. The authors assessed exposure tochloropicrin resulting from the application using a public domain air pollution dispersion model, theIndustrial Source Complex 3 (ISC3). Results. A total of 440 subjects were represented in the interviews,including 324 (73.6%) who reported symptoms possibly or probably related to chloropicrin exposure.Ocular symptoms were present in 302 (93.2%) of the symptomatic cases. Nonocular (usually systemicor respiratory) symptoms occurred in 170 cases (52.5%), but occurred significantly more frequently inresidents who lived within 0.46 miles of the application site. Air-modeling showed a plume of chloropicrinin the affected neighborhoods, with estimated 1-h TWA (time-weighted average) air concentrationsbetween 0.15 and 0.025 ppm. Conclusions. Ocular, respiratory, and systemic symptoms on the eveningof October 5, 2005, corresponded to a plume of chloropicrin, with estimated concentrations as high as0.15 ppm, in the community of Salinas, California. Cases occurred between 0.36 and 2.89 miles fromthe application site. Use of irritant agricultural fumigants near residential neighborhoods can produce arisk of illness for distances more than 2 miles from the site of application. Air modeling is useful forevaluating the relationship between possible exposures and community symptoms.

KEYWORDS. Agriculture, air pollution chloropicrin, eye irritation, respiratory irritation

Terrell Barry is affiliated with the Environmental Monitoring Branch, Department of Pesticide Regula-tion, California EPA, Sacramento, California, USA.

Michel Oriel, MaryLou Verder-Carlos, Louise Mehler, and Susan Edmiston are affiliated with theWorker Health and Safety Branch, Department of Pesticide Regulation, California EPA, Sacramento,California, USA.

Michael O’Malley is affiliated with the Worker Health and Safety Branch, Department of PesticideRegulation, California EPA; and Occupational Health Services, University of California, Davis, California,USA.

Financial disclosure: The authors have no financial interest in the production or sales of chloropicrin orother agricultural chemicals.

This work is based upon reports submitted to the California Pesticide Illness Surveillance Program, andfield investigations performed by the Monterey County Department of Agriculture.

Address correspondence to: Michael O’Malley, MD, MPH, 501 Oak Ave, Davis, CA 95616, USA(E-mail: [email protected]; Phone: 530-757-3200).

Downloaded By: [O'Malley, Michael] At: 18:22 21 January 2010

Barry et al. 25

INTRODUCTION

With limitations on the use of methyl bromideimposed by an international treaty,1,2 the use ofmetam-sodium, chloropicrin, and other fumi-gants has increased. This has been accompaniedby multiple illness episodes in areas wheretreated fields are juxtaposed with housing.3–6

Chloropicrin Mode of Action on Target Pests

Halogenated fumigants, including chloropicrin,are electrophilic chemicals, reacting withnucleophilic amino acids (glutamine, aspar-agines, cysteine, and serine) at or near theactive sites of enzymes in target pathogens ortarget pests.7,8 Used in concentrations greaterthan 2%, chloropicrin is considered an activebiocidal ingredient rather than a warning agent.6

It can be mixed with other halogenated fumi-gants, including methyl bromide (18 products,20% to 55% chloropicrin), dichloropropene (15products, 15% to 60% chloropicrin), and methyliodide (6 products, 0% to 75% chloropicrin).9

There are no registered products mixingmetam-sodium with chloropicrin or other halo-genated fumigants. Experimental combinationsof metam-sodium and halogenated fumigants doshow control of target organisms comparableto that of methyl bromide.10 However, experi-ments show that for most halogenated fumi-gants metam increases both in vitro and soilbreakdown.11

Physical and Chemical Properties

Chloropicrin is also known by its chemicalsynonyms trichloronitromethane and nitrochlo-roform. It is a colorless to faint-yellow oily liquidwith a strong odor described as pungent, sweet,and irritating. It has a molecular weight of164.4 Da (daltons), a boiling point of 112°C,and a melting point of −64°C. Its water solubilityis 1.8 g/L at 20°C; it mixes with benzene, absolutealcohol, and carbon disulfide. It has a vaporpressure of 18.3 mm Hg at 20°C. It has a specificgravity of 1.66 at 20°C, density of 1.65 g/cm3 at20°C.6 It has a vapor density approximately 5.7times that of air.12 Although density affects thelayering of nonmiscible fluids, vapor density

does not affect calculation of pollutant verticaldistribution according to the ideal gas law orGaussian air pollution models.13

In the Industrial Source Complex 3 (ISC3)model, atmospheric stability is the greatestpredictor of vertical dispersion (vertical variationin pollutant concentration). So-called heavy gasmodels account for the effect of gravity onpollutants heavier than air. In a Lagrangianparticle model,14 the tendency of heavy gases tosink downward is described by the equation:dWb/dt = (pollutant density − air density)/pollutant density × G − Wb/Tl,, where Wb = ver-tical component of velocity due to buoyancy, Tl =Lagrangian time scale, and G = the gravita-tional constant. (The term dWb/dt is only onecomponent of the overall model, but predictsthat the pollutant distribution may becomeskewed downwards under conditions of highatmospheric stability.) Because the effect ofgravity is exerted on individual low mass parti-cles, this gravitational effect is generallysmall.14

Eye Irritation and Respiratory Irritation Thresholds for Chloropicrin

Experimental human studies with pesticidesand other industrial products have recentlyproved controversial because some perceivethat the intent of the studies is to evade existingcontrols on pesticide use.15–17 The controversyalso affected a human volunteer study on theirritant effects of chloropicrin.18 State politi-cians and the Natural Resources Defense Councilcriticized the process used to inform volunteersof possible study risks.16,19 Principal studyfindings included an estimate of the thresholdof odor perception in relation to the thresholdsfor ocular and respiratory irritation. The medianodor threshold for all subjects was 700 ppb. Theperception of odor diminished with prolongedexposure while the perception of irritationincreased.

For brief exposure (5 to 30 s), eye irritation(or at least “chemesthesis”—detection of expo-sure by the eye) occurred in 50% of volunteersubjects exposed to 700 ppb of chloropicrin. Ofthe 62 subjects tested, 10% to 15% (dependingupon the site of exposure) failed to detect 1200


26 COMMUNITY EXPOSURE FOLLOWING A DRIP-APPLICATION OF CHLOROPICRIN

ppb of chloropicrin (the highest concentrationstested in the study). For exposures lasting 20min, the minimum concentration detectable by50% of the subjects was 75 ppb. The noobserved effect level (NOEL) for this portion ofthe study was 50 ppb. For 1 h, exposures of 100and 150 ppb produced subjective eye irritationin most subjects. Using a standard 10-folduncertainty factor,20 an estimated NOEL for a1-h exposure to chloropicrin (calculated fromthe 100 ppb lowest observed effect level[LOEL]) would be 10 ppb.

The distinction between chemesthesis andirritation made by Cain18 is not made by otherspecialists in sensory irritation. Dalton, forexample, uses the terms “chemesthesis” and“irritation” interchangeably, making the pointthat the onset of sensory irritation is highlyinfluenced by subjective factors.21

In the subjects studied by Cain18 (selectedfor absence of asthma, allergic rhinitis, andother common respiratory conditions), respiratoryirritation was not quantifiable for brief expo-sures above 1 ppm. Likewise, no upper or lowerrespiratory symptoms were noted in either the20-min (75 ppb) or the 60-min (100 and 150ppb) exposures.

Regulatory Controls on Chloropicrin Exposure

Existing regulatory controls on chloropicrinall appear to be based on the 0.1 ppm thresholdlimit value (TLV) for an 8-h exposure (a time-weighted average [TWA]) set by the AmericanConference of Governmental IndustrialHygienists (ACGIH)22 based upon experimentalstudies performed on human volunteers duringWorld War I (WWI). The 0.1 ppm 8-h TWA isalso the permissible exposure limit (PEL) set bythe US Occupational Safety and Health Admin-istration (OSHA) and the recommended exposurelimit (REL) suggested by the National Institutefor Occupational Safety and Health (NIOSH). Itis also the air concentration indicated as a triggerfor respiratory protection on labels on currentchloropicrin fumigants and warning agents.23

The US Environmental Protection Agency(EPA) has recently proposed an Acute ExposureGuideline Level-1 (AEGL-1) of 0.05 ppm

based upon the Cain human exposure study.24

This was based upon the no observed adverseeffect level (NOAEL) for the 20-min exposureinterval from the study by Cain describedabove.

The TLVs are controversial as occupationalstandards.25–28 The TLV for chloropicrin isbased upon WWI-era studies with humanvolunteers,6,22 but is not based upon a no-effectlevel. The 8-h time interval used in the standardrepresents another deficiency: peak levels caus-ing acute irritation can easily be obscuredwithin an 8-h interval with an average exposureat or below the 0.1 ppm standard.

METHODS

This paper describes an October 2005 com-munity exposure to chloropicrin in the Californiacentral coast community of Salinas. As in priorepisodes,3–5 dispersion air modeling was usedto evaluate concentrations of chloropicrinpresent in the community relative to reportedirritation thresholds. The effect of an accidentalpostapplication release of residual chloropicrin(from an incompletely evacuated sprinklerirrigation line) was also evaluated and comparedto the downwind concentrations expected fromthe fumigant intentionally applied to the treatedfield.

Background

At approximately 11 AM on October 5, 2005,an agricultural application service companyinitiated treatment via drip application of a 12.1acre tarped field (preplant for strawberries,designated as block 20), with a formulation of94% chloropicrin; the fumigation took a total of4 h at a rate of 11 lbs/min. This represented atotal of 2640 lbs, or 203 lbs/acre (approximatelythe midpoint of the application rates, 100 to 300lbs/acre, specified on the product label).

Following completion of the drip application,the irrigation lines were flushed for 45 min toclear the irrigation lines of residual chloropicrin.The label specifies that the irrigation linesshould be flushed with untreated water afterthe application, but states only that the


Barry et al. 27

maximum amount of water/acre for the entireapplication, including the flush, should notexceed 40,000 gallons/acre—1.5 acre inches.This line flushing was followed by a “watering-in” sprinkler application to slow the escape ofthe fumigant from the treated field. The exacttimeline of each of these events is unknown;however, the “watering-in” sprinkler applica-tion began sometime about 5:30 PM or shortlyafterwards. Auxiliary pumps were used to boostthe sprinkler pressure between approximately7 PM and 9 PM. The sprinkler treatment used thesame main irrigation pipes connected earlier tothe drip application lines. One of the crewmembers described a noticeable odor ofchloropicrin during the postapplication “water-ing-in”: “At about 5:30 PM, I smelled the picafter the sprinklers had been turned on, butbefore the boosters had been fired up.”Although there was no chloropicrin odorpresent at the time, the mechanical pressureboosters were started, the crew observationsraised concern that residual chloropicrin in themain irrigation pipes and in side pipes to otherfields on the irrigation system had traveleddownwind. An event reconstruction (using reddye in place of chloropicrin) confirmed thatresidual chloropicrin was in the main at the startof the “watering-in” sprinkler irrigation. Duringtwo reconstruction tests, red dye appeared inthe water for approximately the first 37 to 60min of the “watering-in” period.

Emergency Calls and Neighborhood Case Survey

At 8:14 PM on October 5, 2005, a neighbor-hood resident called the Monterey Countyemergency response system to complain thatthe air outside his home was making his eyesburn. He reported that his neighbors had similarsymptoms. Over the next hour, 14 calls withsimilar complaints were received. The last callwas received at 10:08 PM.

On October 6, Monterey County Departmentof Agriculture and Department of Health eval-uated the pattern of calls to the 911 emergencyresponse system, noting that many calls camefrom homes near the Natividad Creek drainage.(The distribution along the creek drainage also

suggested to investigators that the cases mighthave occurred most frequently in areas of rela-tively low elevation.)

Between October 8 and October 10, Depart-ment of Agriculture staff surveyed the neighbor-hoods adjacent to the creek and otherneighborhoods identified as the source of one ormore emergency calls (Figure 1). At least oneadult member of each potentially affected house-hold was interviewed either by telephone orin-person. For each address surveyed, the locationwas identified by geographic informationsystems (GIS) coordinates, distance relative tothe treated field, and elevation above sea level.

The interviews focused on symptoms experi-enced on October 5, but did not include questionsregarding outdoor activities. Recorded symptomsincluded eye irritation, nasal irritation, cough,dizziness, sore throat, shortness of breath, rashor itching, occurrence of odor, headache, andnausea or vomiting. For residents who soughtmedical treatment, reports submitted by attendingmedical providers to the California PesticideIllness Surveillance Program (pesticide illnessregistry) were also reviewed.

Cases in the affected neighborhoods withsymptoms consistent with the chloropicrintoxidrome (eye irritation with or without sys-temic or respiratory symptoms) were classifiedas probably related to the episode. A few caseswith eye irritation were classified as possiblyrelated to the outbreak because the reported timeof onset was the morning following the incident.

Individuals with systemic or respiratorysymptoms without eye irritation were generallyclassified as possibly related to the episode, butindividuals with outdoor exposure, or who likelyhad increased susceptibility (e.g., asthma), wereclassified as probable cases. Based upon groupconsensus of several reviewers, isolated upperrespiratory irritation was also considered proba-bly related in one case where eye irritation waspresent in another household member.

Estimated Population in the Affected Neighborhood

The MARPLOT GIS program from theNational Oceanic and Atmospheric Administra-tion (NOAA) allows estimation of exposed



populations within areas exposed to environ-mental spills by connecting GIS information toUS census tract information. For purposes ofthis study, we estimated the area in the path ofthe chloropicrin plume using the MARPLOTpolygon tool.29

Air Modeling Methods

None of the local agencies responding to theOctober 5 incident had the resources or trainingto collect air samples for chloropicrin, althougha direct-reading photoionization detector wasused by Monterey County EnvironmentalHealth staff to check for the presence of methylbromide.*

We employed the US Environmental Protec-tion Agency (US EPA) Industrial SourceComplex Short-Term Version 3 (ISC3), a

steady-state Gaussian plume model, to estimatechloropicrin air concentrations. Details of themodeling techniques are given in a previouspublication.3 The critical inputs to the modelinclude field flux (which we estimated from aprior chloropicrin drip application study30),wind speed, wind direction, and atmosphericstability (a measure of contaminant tendency todisperse vertically). We obtained weather infor-mation from a California Irrigation ManagementInformation System (CIMIS) station 116,located slightly northwest of Salinas, approxi-mately 4.8 miles from the intersection ofBoronda and Constitution. Terrain betweenCIMIS station 116 and incident location iseither open agricultural land or residentialdevelopment. The elevation at CIMIS station116 versus the intersection of Boronda andConstitution is approximately 66 and 99 ft

FIGURE 1. Distribution of community illnesses, October 5, 2005, Salinas, California. Treated field:12.1 acres fumigated prior to planting strawberries—94% chloropicrin applied for 4 h at a rate of11 lbs/min, a total application of 2640 lbs, or 203 lbs/acre. Circles: emergency calls receivedbetween 8:14 PM and 10:15 PM. Hexagons: Cases with eye irritation only. Squares: Respiratory orsystemic symptoms and eye irritation. Triangles: Respiratory or systemic symptoms but no eyeirritation. Crosses: residents with no reported symptoms on interview.


Barry et al. 29

above sea level, respectively. Thus, weatherdata from CIMIS station 116 is likely a validrepresentation of conditions in the vicinity ofthe incident. Data from the CIMIS station 116indicated that the wind speed present in Salinasduring the evening of October 5, 2005 (2 to 3.3mph) corresponded with atmospheric stabilityclass F (highly stable, with minimal tendencyfor vertical dispersion). Wind came from thenortheast during most of the incident (Table 3).

The modeling was conducted in three phasesin order to estimate the chloropicrin flux from theplanned application (designated as the applicationsource), to estimate the flux contribution from theaccidental release of chloropicrin from the irriga-tion lines during the postapplication water treat-ment (designated as the sprinkler source), and thecombined flux from both sources.

Sprinkler Source

We estimated the potential contamination fromthis source initially by calculating the volume ofresidual chloropicrin in the main irrigation lines.We assumed that the entire length of main irriga-tion pipe was 8 inches in diameter (although anunknown portion was either 6 inches or 4 inches).

The estimated length of the main irrigationpipe from the injection point to Block 20 isapproximately 4370 ft. The volume of the pipe iscalculated as: pr2l = ft3 = p(0.33)2(4370) = 1495ft3 = 11,183 gallons.

The mass of chloropicrin available to bereleased through the sprinklers from the mainirrigation pipe is calculated based on theassumption that the all the water in the pipe is atthe application rate concentration of 885 ppmchloropicrin. This maximum mass of chloropicrinis calculated below:

Therefore, approximately 82 lbs of chloropicrinwas the estimated maximum mass available to be

released through the sprinkler heads andapplied directly to the surface of the field(tarped beds and furrows). The irrigation spe-cialist that designed the irrigation system ini-tially calculated that 90 min would be requiredadequately flush the drip system. However, it islikely 90 min was not adequate. The subsequentevent reconstruction (using red dye in place ofchloropicrin) confirmed that residual chloropi-crin was in the main at the start of the “water-ing-in” sprinkler irrigation. Further, during thereconstruction at the start of the watering, in thesprinkler water was deep red, indicating a sig-nificant lack of drip irrigation line flushing.Because the drip lines were flushed for only 45min and the reconstruction indicated that signif-icant chloropicrin mass remained in the mainirrigation pipe, our calculation assumed that thechloropicrin mass had been reduced by onlyhalf when the sprinklers were initially turnedon. It was also assumed that the mass of chlo-ropicrin released from the sprinklers wasreleased to the entire 12.1-acre block. Basedupon these calculations an “application rate”from the sprinklers was calculated as: 41.2 lbs/12.1 acre = 3.4 lb/acre = 0.382 g/m2.

This estimate does not include any chloropicrinthat may have been in water in side-lines off themain sprinkler line. Because irrigation watercontinued to be applied to the field after the initialchloropicrin deposition, the chloropicrinsolution was continually diluted and rinsed offthe tarped surface of the beds. Some of thechloropicrin would also have percolated intothe soil in the furrows.

Application Source

As indicated above, an estimate of thechloropicrin flux from the 2640 lbs applied tothe treated field was based upon a 2004 moni-toring study performed by the chloropicrinmanufacturers. Use of the ISC3 model to estimateflux from similar applications has beendescribed previously for air pollution eventsinvolving both chloropicrin4,6 and the metam-sodium by-product methyl isothiocyanate(MITC).3,5

Initial chloropicrin air concentration esti-mates from the ISC3 model are presented here

lbs chloropicrin gallons 2.2lb/kg

1 kg/1,000,000 mg

3.785

= × ××

LL/gal 885 ppm

lbs chloropicrin 11183

ppm

×

= × × ×=

−( . )8 327 10

885

6

882 4. lbs.



as 1-h TWA concentrations, in accordance withthe 1-h intervals used for reporting the availableweather data. Peak-to-mean estimationtechniques were used to obtain estimates of airconcentrations over shorter averaging periods(e.g., 3- and 1-min). Because mean concentra-tions are the result of integration over manyshort-term peak conditions during the samplinginterval, a definable relationship exists betweenthe peaks and the mean.31,32

GIS Graphic Analysis and Statistical Analysis

Graphic comparison of the distribution ofcases with the ISC3 chloropicrin concentrationisopleths employed software from ArcGIS,version 8.2 (ESRI) and a commercially availablecolor aerial photograph (Google Earth Profes-sional). The ArcGIS shape file allowed directoverlay of chloropicrin concentration isoplethsand community street map on to the aerialphotograph. Concentration isopleths (analogousto the elevation contours on a contour map)were produced from the ISC3 plot file using thecontour map feature of Surfer7 (Golden Software,1999). We performed mapping of cases associatedwith individual addresses using decimal latitudeand longitude coordinates available from GoogleEarth.

We evaluated statistical relationships usingthe analysis module of Epi Info.33,34 The princi-pal outcome analyzed was the occurrence ofsymptoms expected to result from low-doseexposure (eye irritation only)18 and thoseexpected to result from high-dose exposure(most commonly eye irritation, accompanied byrespiratory or nonspecific systemic symptoms).This was defined as follows:

Unrestricted analysis: The high exposuresymptom group included all cases that hadnonocular symptoms—including a smallpercentage of cases with skin, respiratorysymptoms, and/or systemic symptoms butno eye irritation.

Restricted analysis: The high-exposuresymptom group was limited to cases thathad eye symptoms, accompanied byskin, respiratory symptoms, or systemic

symptoms. The restricted analysis wasconducted because of concern that someof those with isolated systemic or respi-ratory symptoms might have representedconditions unrelated to the exposure.

The unrestricted and restricted evaluations ofrisk factors for “high-exposure” and “low-exposure” symptom patterns was performedbecause it appeared that the ascertainment ofboth symptomatic and asymptomatic individualswas not sufficiently systematic and complete toallow estimation of the actual incidence of ill-ness by neighborhood or incidence by distancefrom the treated field (Figure 1).

Statistical tests included a chi-square for lineartrend in proportion for case distributions byelevation above sea level and distance from thetreated field. We also calculated an odds ratio(OR) comparing the lowest tertile (of elevationor distance) with the highest tertile. We evaluatedthe simultaneous effect of both variables usinglogistic regression.

RESULTS

Neighborhood Case Survey

Interview forms were completed andreviewed for 143 separate residences in theneighborhood downwind of the treated field.(This represented 26% of the estimated 655household in the affected neighborhoods.) Onemember of the county hazardous materialsemergency response crew also reported tran-sient eye symptoms slightly more than 0.5miles from the edge of the treated field.Coworkers reported to have similar symptomsdid not file complaints and were not specificallyidentified. A total of 440 subjects were repre-sented in the interviews (13.1% of the estimated3363 persons in the affected neighborhoods).Three hundred twenty-four subjects (73.6%)reported symptoms possibly or probably relatedto chloropicrin exposure, and 24 subjects(5.5%) had symptoms unrelated, unlikely to berelated, or with information too limited to classify(Table 1). Ninety-two subjects (20.9%) inter-viewed reported no symptoms. Of the 324


Barry et al. 31

subjects with symptoms possibly or probablyrelated to the incident, 154 (47.5%) had onlyeye symptoms and 170 (52.5%) had nonocular(skin, respiratory, or systemic) symptoms,including 148 (87.1%) with simultaneous eyesymptoms. Eye symptoms affected a total of 302(93.2%) of the 324 symptomatic individuals.

A total of 117 (36.1%) subjects reportedrespiratory symptoms, including 32 (27.4%) withsymptoms of cough or shortness of breath poten-tially related to the lower respiratory tract. Theremainder reported only upper respiratory irrita-tion. The cases with reported lower respiratorysymptoms included a 51-year-old man with pre-existing asthma who reported experiencing coughand shortness of breath on October 5. He appar-ently did not seek medical treatment but was stillsymptomatic when interviewed 5 days after theincident. A 36-year-old man with preexistingasthma reported experiencing a cough for 12 hafter the incident. A total of 82 subjects (25.3%)reported systemic symptoms (most frequentlynausea, headache, vomiting, or dizziness).

Of the 324 subjects with symptoms judged asrelated to the illness, 15 (4.6%) reported seekingmedical evaluation at hospitals or clinics nearSalinas prior to being interviewed after theincident, with minimal variation by distance

from the treated field (3.9% to 5.4%). Thoseseeking treatment included two cases of isolatedeye irritation, two with isolated respiratorysymptoms, and two with only systemic symp-toms. One subject reported burning eyes and asore throat, but sought treatment principally forfalse labor symptoms. Another subject soughttreatment for a nose bleed and did not haveother symptoms, including eye irritation. Threereported shortness of breath, potentially repre-senting lower respiratory irritation.

Distribution of Cases by Distance and Elevation

The 324 chloropicrin-related cases occurredscattered in a track or line south and west of thetreated field, up to a distance of approximately2.9 miles. One hundred and three cases (31.7%)occurred within 0.46 miles, and an additional110 cases (34.0%) occurred between 0.47 and1.01 miles of the treated field. The remaining111 related cases (34.3%) occurred at distancesof 1.02 to 2.89 miles from the treated field.

As shown in Table 2, nonocular symptoms(usually systemic and or respiratory symptoms)occurred in 69 (67.0%) of 103 residents livingat distance of 0.46 miles or less from the edge of

TABLE 1. Subjects Interviewed in Investigation of Salinas, October 5, 2005, Chloropicrin Exposure

Symptom complex

Relationship between symptoms and case classifications

Probable Possible Total related cases No symptoms Other cases* Total

Eye irritation only 154 154 154Eye irritation, with respiratory, skin, or systemic symptomsEye/skin 1 1 1

Respiratory/eye 75 1 76 76Respiratory/eye/skin 1 1 1Systemic/eye 43 1 44 44Systemic/respiratory/eye 25 1 26 2 28

Respiratory, systemic, or skin symptoms without eye irritationRespiratory 2 8 10 1 11Systemic 8 8 5 13Systemic/respiratory 1 3 4 2 6Skin 1 1

Total Symptomatic 302 22 324Asymptomatic 92 92Unknown illness status because of

limited information13 13

Total subjects interviewed 302 22 324 92 24 440

*Unlikely to be related, unrelated, or unable to classify.



the treated field, in 60 (54.5%) of the 110 resi-dents living between 0.47 and 1.01 miles of thetreated field, and in 41 (35.5%) of 111 residentsliving at distances of 1.02 miles or more. Thechi-square for linear trend in proportions wassignificant (p < .001), and the OR(distance, 1st tertile vs

3rd tertile) for risk of nonocular symptoms was 0.29(95% CI 0.16, 0.53; p < .001). We noted a verysimilar relationship in the restricted analysisOR(distance, 1st tertile vs 3rd tertile) = 0.20 (95% CI 0.11,0.39; p < .001). The distribution of cases, accord-ing to symptom pattern and distance from thetreated field, is shown in Figure 1.

The treated field ranged in elevation from105 to 118 ft above sea level, and householdsin the affected neighborhoods ranged in eleva-tion from 49 to 125 ft above sea level. The fre-quency of nonocular (systemic andrespiratory) symptoms varied by elevation,

ranging from 37.9% for occupants of resi-dences 47 to 74 ft above sea level, to 60.0%for occupants of residences greater than 82 ftabove sea level (Table 2). The chi-square forlinear trend in proportions was significant (p <.001). The OR(elevation, 1st tertile vs 3rd tertile) for riskof nonocular symptoms in the unrestrictedanalysis (n = 324) was 0.41 (95% CI 0.23,0.73; p < .001). In the restricted analysis (n =302), OR(elevation, 1st tertile vs 3rd tertile) for risk ofnonocular symptoms was 0.36 (95% CI 0.20,0.67; p < .001).

When both distance and elevation wereentered in a logistic regression model, only thedistance from the treated field remained signifi-cant. The OR(distance, coded by tertiles) was 0.59(95% CI 0.4298, 0.8232; p = .002), indicating aprotective effect of increasing distance from thetreated field against systemic and respiratory

TABLE 2. Effect of Distance From Treated Field and Elevation Above Sea Level

Distance fromtreated field, miles

Ocular symptoms only

Ocular symptoms,additionalrespiratory/systemic

or skin symptoms

Respiratory/systemicor skin symptoms

without ocular symptoms

All cases withnonocularsymptoms % Total

0.36–0.46 34 67 2 69 67.0 1030.47–1.01 50 53 7 60 54.5 1101.02–2.89 70 28 13 41 36.9 111Total 154 148 22 170 52.5 324

Recorded terrrain elevation, feet above sea level

Ocular symptoms Only

Ocular symptoms, additionalrespiratory/systemic

or skin symptoms

Respiratory/systemicor skin symptoms

without ocular symptoms

All cases with nonocular symptoms

% Total

47–74 72 35 9 44 37.9 11675–82 40 57 6 63 61.2 103>82 42 56 7 63 60.0 105Total 154 148 22 170 52.5 324

TABLE 3. Weather Data From California Irrigation Management Information System (CIMIS) Station 116 (Monterey Bay, Salinas North) for Evening of October 5, 2005

Hour, Pacificdaylight time Wind speed “To” wind direction “From” wind direction SD (degrees) Stability class

6 PM–7 P.M 1.16 m/s, 2.6 mph 83.5 263.5 17.9 E7 PM–8 PM 0.98 m/s, 2.2 mph 202.2 22.5 64.2 F8 PM–9 PM 1.47 m/s, 3.3 mph 225.9 45.9 13.9 F9 PM–10 PM 1.16 m/s, 2.6 mph 230.3 50.3 21.2 F10 PM–11 PM 1.03 m/s, 2.3 mph 299.0 118.8 36.7 F

Note. Wind directions: 0°, 360° = north; 90° = east; 180° = south, 270° = west; the source of wind (or “from”direction) reported by CIMIS; the “to” direction is employed in the ISC3 air model.


Barry et al. 33

symptoms. The effect of distance appearedeven more clearly in the restricted analysis: theOR(distance, coded by tertiles) was 0.49 (p < .001).Elevation did not appear significant in eitherthe unrestricted analysis (OR(elevation, coded by

tertiles) = 1.22, 95% CI 0.8915, 1.6743; p = .21)or the restricted analysis (OR(elevation, coded by

tertiles) = 1.18, 95% CI 0.8518, 1.643; p = .32).

Air Modeling Estimates of Chloropicrin Concentrations

Figure 2 shows the estimated 1-h TWA chlo-ropicrin air concentration isopleths originatingfrom the chloropicrin mass release through thesprinklers alone for the period between 2000and 2100 hours on October 5, 2005. Theestimated 1-h TWA chloropicrin air concentra-tions in the areas where the 911 calls originatedwere below 0.10 ppm.

Figure 3 shows the estimated air concentrationsfor the same time period from the applicationsource. The estimated 1-h TWA chloropicrinair concentrations ranged from 0.025 to 0.15ppm. A plot of the composite of the flux fromthe chloropicrin on the surface of the field andthe flux from the application itself showed thean identical pattern to that shown in Figure 3,with the estimated concentrations ranging from0.025 to 0.15 ppm. Based upon peak-to-meanestimates, the short-term (3-min TWA) concen-trations of chloropicrin may have reached ashigh as 0.6 ppm (Table 4).

DISCUSSION

The distribution of emergency calls andcases identified in the neighborhood surveycorresponded temporally and geographically

FIGURE 2. Chloropicrin air concentrations (ppm) for the interval 8 PM to 9 PM associated withpossible release of 84 lbs of chloropicrin from sprinklers used for postapplication water treatment.Hexagons: Cases with eye irritation only. Squares: Respiratory or systemic symptoms and eyeirritation. Triangles: Respiratory or systemic symptoms but no eye irritation. Chloropicrin isoplethconcentrations (ppm) as labeled on figure.



with the presence of a plume of chloropicrinfrom the field treated by drip irrigation onOctober 5. Estimated 1-h chloropicrin air con-centrations exceeded both the existing 100 ppbthreshold limit value and the LOEL of 75 ppbfor 20 min of continuous exposure identified inthe recent human volunteer study.18

Careful attention to label-required applica-tion techniques and attention to control mea-sures recommended by pest control advisers

play an important role in minimizing off-sitemovement from applications of chloropicrinand other soil fumigants. Quantitative analysisbased upon the ISC3 modeling indicates thatthe failure to follow recommended applicationtechniques likely accounted for only a portionof the offsite movement of the chloropicrinthat caused the Salinas 2005 episode. As indi-cated in Figure 2, the plume of chloropicrinfrom the postapplication sprinkler irrigation

FIGURE 3. Estimated chloropicrin air concentrations (ppm) associated with the drip applicationmade to treated field, Salinas, California (identical to plot estimating combined effect of dripapplication and sprinkler source). Hexagons: Cases with eye irritation only. Squares: Respiratoryor systemic symptoms and eye irritation. Triangles: Respiratory or systemic symptoms but no eyeirritation. Chloropicrin isopleth concentrations (ppm) as labeled on figure.

TABLE 4. Relationship Between 1-Hour TWA Concentrations (ppm) and Estimated Peak Concentrations (ppm)

1-h TWA (ppm) 30-min TWA (ppm) 10-min TWA (ppm) 3-min TWA (ppm)

0.05 0.06 0.11 0.200.10 0.13 0.23 0.400.15 0.19 0.34 0.60

Note. TWA, time-weighted average.


Barry et al. 35

(“watering-in”) could have accounted for onlythe cases in the immediate vicinity of thetreated field. The plume from the drip applica-tion moved a much greater distance offsite(Figure 3).

The 1-h concentrations from the combinationof the flux from the drip application and the fluxfrom the accidental sprinkler release (Figure 3)reached as high as 0.15 ppm in the neighbor-hoods closest to the treated field. As demon-strated in Table 2, these neighborhoods had asignificantly higher frequency of respiratoryand systemic complaints than more distantareas where most of those affected only had eyesymptoms. Short-term concentrations peaks mayhave reached as high as 0.6 ppm of chloropicrin(Table 4).

Likelihood of Similar Episodes

The occurrence of application-related casesmore than a mile down wind of the applicationsite has implications for the regulation offumigants containing chloropicrin. Numerouscommunity and occupational episodes associatedwith the off-site movement of chloropicrinfumigant mixtures have previously been docu-mented.6 The juxtaposition of new housing andagricultural land may prove problematic inother communities.

Limitations of the Data

As in previous community exposures tofumigants, available resources precluded acomplete survey of the affected neighborhoods.The interview sample represented 26% of theestimated households in the path of the plumeand 13% of the population of 3353 estimatedwith the GIS tool. Because the sampling wasbased upon the location of the “911” emergencycalls, it is uncertain how many cases occurredin neighborhoods in the path of the chloropicrinplume from which no calls were recorded.

The collection of symptom information byquestionnaire in the aftermath of a large-scalecommunity exposure can be problematic,occasionally yielding information influencedby community controversy. In this instance,the event did result in press coverage,35,36 butcontroversy appeared remarkably absent, and

slightly less than 4% of those reported to beaffected sought medical treatment. The pattern ofsymptoms, with eye irritation occurring in 94%of those affected, corresponds closely with previ-ously reported episodes involving chloropicrinand with the results of the human experimentalstudy reported by Cain.18 The predominance ofisolated eye irritation in neighborhoods farthestfrom the treated field (Table 2) also accords withthe findings of the study by Cain.

Although experimental data and prior com-munity illness episodes have demonstrated that5% to 10% of chloropicrin exposures do notresult in eye irritation, some ambiguity remainsin interpreting the 22 cases with respiratory,skin, or systemic symptoms without anyreported ocular symptoms. These cases couldrepresent a response to odor or symptoms ofsome unrelated illness. The data from the Sali-nas 2005 episode provide some support for thishypothesis in that the inverse associationbetween distance from the treated field and theoccurrence of the “high-exposure” toxidrome(Table 2) is stronger (OR = 0.20) in therestricted analysis, compared with the unre-stricted analysis (OR = 0.29).

Estimates of exposures from the ISC3atmospheric dispersion model provide areasonable estimate of average exposures toresidents in the affected neighborhoods. Itappears that the amount of chloropicrin fromthe sprinkler source was small in relation tothe amount of chloropicrin from the applica-tion source. However, the uncertainty in chlo-ropicrin flux estimates cannot be readilyquantified because the estimates were basedonly a single study.30 Based upon studies withmetam-sodium and other fumigants, the maxi-mum likely deviation of the flux from theapplication source, relative to the single avail-able study, was approximately 20%.

The ISC3 model does not account for terraineffects or pollutants with densities significantlygreater than air. There were small variations inelevation in the path of the plume. The treatedfield (Block 20) was at an elevation of 118 ft,whereas areas where 911 calls originated were atelevations ranging from 60 to 90 ft. This topo-graphic feature may have lead to localized higherconcentrations than the ISC3 model predicted.37



The Lagrangian particle model14 and other heavygas models include the potential for downwardbias in the vertical distribution of the relativelyheavy pollutant plume. For chloropicrin, thisdownward bias is assumed to be small or nonex-istent. In support of this assumption, analysis ofthe distribution of respiratory and systemicsymptoms relative to isolated ocular symptomsshowed the reverse of the expected effect(Table 2). Locations more than 82 ft above sealevel (highest tertile) had a 60.1% prevalence ofnonocular symptoms, compared with a 36.4%prevalence for locations of 74 ft or less in eleva-tion (lowest tertile). Although this suggests anupward bias in the plume distribution, this find-ing may have been an artifact. There was noassociation between the occurrence of nonocularsymptoms and elevation when distance from thetreated field was accounted for simultaneously.

CONCLUSIONS

Residual chloropicrin in irrigation lines usedfor a postapplication water treatment was initiallyinvestigated as the possible cause of the event.Although the postapplication water treatmentcaused an estimated 42 lbs of chloropicrin tobecome airborne, the drip application contributeda far larger amount of the chloropicrin thatmoved offsite. The October 2005 Salinas episodeunderscores the risk of applying a volatile fumi-gant with a low irritation threshold immediatelyadjacent to populated areas.

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